It is known from European Patent Application No. 170,311 to dimerize an alpha-alkene having in the range of from 2 to 12 carbon atoms per molecule in the presence of a catalytic system formed by combining, in the presence of water, an alcohol, or a carboxylic acid:
(a) a palladium(II) compound, PA1 (b) a chelate ligand comprising a compound containing as coordinating atoms at least two nitrogen atoms which are connected through a chain comprising two carbon atoms, and PA1 (c) a compound containing an anion of an acid, with the exception of hydrohalogenic acids. PA1 (a) a palladium(II) compound, PA1 (b) a chelate ligand comprising a compound containing as coordinating atoms at least two nitrogen atoms which are connected through a chain comprising two carbon atoms, more than 2.0 mol of the chelate ligand per gram-atom of palladium(II) being used, PA1 (c) a protonic acid, with the exception of a hydrohalogenic acid, and PA1 (d) a salt of copper, iron, zinc, tin, manganese, vanadium, aluminium or of a metal of Group VIB of the Periodic Table of the Elements, with the exception of a halide. PA1 (a) a palladium(II) compound, PA1 (b) a chelate ligand comprising a compound containing as coordinating atoms at least two nitrogen atoms which are connected through a chain comprising two carbon atoms, more than 2.0 mol of the chelate ligand per gram-atom of palladium(II) being used, PA1 (c) a protonic acid, with the exception of a hydrohalogenic acid, and PA1 (d) a salt of copper, iron, zinc, tin, manganese, vanadium, aluminium or of a metal of Group VIB of the Periodic Table of the Elements, with the exception of a halide.
The reaction mixture obtained by means of this known process may comprise a two-phase liquid system: a liquid dimer phase and a liquid solvent phase containing the catalytic system. Both phases can easily be separated by means of mechanical separation and the separated solvent phase containing the catalytic system can be used for dimerizing further quantities of alpha-alkenes.
It has been observed that the dimer phase contains a portion of the chelate ligand and the solvent phase has a correspondingly reduced content thereof. This reduced content of chelate ligand may lower the catalytic activity of the catalytic system, particularly when considerably less than 2 mol of chelate ligand per gram-atom of palladium(II) remains.
Starting this known process by using more than 2 mol of the chelate ligand per gram-atom of palladium(II) would compensate for said loss of chelate ligand, but renders the catalyst less active.
A novel catalytic system has now been found that is surprisingly active when more than 2 mol of the chelate ligand per gram-atom of palladium are used.